import java.util.HashMap;
import java.util.Map;

public class Text5 {
    // 1419 数青蛙
    public int minNumberOfFrogs(String c) {
        char[] croakOfFrogs = c.toCharArray();
        String t = "croak";
        int n = t.length();
        int[] hash = new int[n];

        Map<Character,Integer> Index = new HashMap<>();
        for(int i = 0; i < n; i++){
            Index.put(t.charAt(i),i);
        }

        for(char ch : croakOfFrogs){
            if(ch == t.charAt(0)){
                if(hash[n-1] != 0)
                    hash[n-1]--;
                hash[0]++;
            } else {
                int i = Index.get(ch);
                if(hash[i-1]==0)
                    return -1;
                hash[i-1]--;
                hash[i]++;
            }
        }

        for(int i = 0; i < n-1; i++){
            if(hash[i] != 0){
                return -1;
            }
        }

        return hash[n-1];
    }
}
